A random sample of 47 students studied for an average of 7.1 hours last week. If the population standard deviation is 1.2 hours, what is the 90% confidence interval for the population mean?
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.05) = Z = 1.645
90% = mean ± 1.645 SEm
SEm = SD/√n